a. Create a base class named Rectangle containing length and width data members. From this class, derive a class named Box with another data member named depth. The member functions of the base Rectangle class should consist of a constructor and an area() function. The derived Box class should have a constructor, a volume() function, and an override function named area() that returns the surface area of the box
b. Include the classes constructed for Exercise 7a in a working C++ program. Have your program call all the member functions in each class, and verify the results manually.